@media (min-width: 961px) {

  .t-feed__container {
      max-width: calc(100% - 200px); /* по ~100px с каждой стороны */
      margin-left: auto;
      margin-right: auto;
  }

  .t-feed__post {
      margin-left: 20px;
      margin-right: 20px;
      max-width: calc(25% - 40px);
  }

}